1. Field of Invention
The present invention relates generally to systems for controlling one or more local displays via a remote transmitter device, but more particularly to such systems useful for sending information from one of many remote locations to a central receiving station in such a manner that the receiving station is capable of detecting the point of origin of the information without the need for further communication with the transmitting station.
2. Description of the Related Art
In many situations it is desirable to have a system that will allow people at multiple locations to signal someone at a central location when assistance is desired. An example of such a situation is in a restaurant where customers may need to summon a waiter or waitress to their table. This example will be used in this application to explain the function of the invention, but other examples of similar situations are in retail stores, manufacturing plants and health care facilities, to name but a few.
In the industry and related art, it is important to understand the major distinction between the two major independent divisions of technology, and the unique incorporation of one such division into present invention and the use of the other such division in the art to which the invention relates. The known signalling systems comprising the art to which the invention relates are constructed of components to operate in accordance with the principle of frequency shift keying or amplitude modulation. Frequency Shift Keying (FSK) communicates information in binary one and zero format by utilizing two different frequencies (one frequency equal to a binary one, the other frequency equal to a binary zero) and pulsing between the two frequencies to communicate information in a binary code. Frequency Modulation (FM), on the other hand, shifts the frequency of a carrier signal in a range between a specified low frequency and a specified high frequency in order to replicate and communicate an analog signal. Devices configured for frequency shift keying/modulation are believed to provide one method of remote location communication, and devices incorporating pulsed width modulation provide another method remote location communication.
Frequency shift keying and pulsed width modulation are not compatible. The structure of such devices are for the most part not interchangeable, and the operation of one device cannot be modified to perform the functions of the other. Therefore, frequency modulation and pulsed width modulation are believed by those skilled in the industry as mutually exclusive in structure and operation.
Frequency modulated devices are known to have operational limitations relating to range of operation, the need for a polling function and the separation distance of the transmitter/receiver components and the central receiving/transmitting station. Such limitations are known to cause errors in signal transmission. Pulsed width modulation, on the other hand, is believed to enable improved message transmission and reception over frequency modulated devices, and does not require structure to enable a polling function.
U.S. Pat. No. 4,777,488 granted to Carlman, Jr. et al., incorporated by reference as if fully set forth herein, is an example of a device that uses frequency modulation to modulate the information carrier. The Carlman patent is directed to a restaurant service request communication system. Carlman using frequency modulation and a polling technique to effectively slot the messages in a certain predetermined order which is likely to be different than the order in which they are sent or received.
Carlman's central receiver at the central receiving station continuously monitors, when not in a wait state, the single frequency transmission for any signal, then polls the signal string in order to determine the position a signal message is in line (ahead of or behind other messages), holds and then decodes the position in line to reveal the corresponding location. Carlman also uses a confirming message sent back from the central receiving station to where the signal is thought to have been originated in order to verify the intended location of the message in the preselected que.
The Carlman carrier is frequency modulated with two separate tones. The signal is sent by a transmitter and then recovered by the receiver and converted back into on and off pulses. In amplitude modulation, about 25% of the power is contained in the modulated signal and 75% in the carrier.
The Carlman system contains a transmitter and a receiver at each remote location. The remote transmitter is only allowed to send a signal (message) at a specific time or sequence and then must wait for an acknowledgement signal to be sent from the central receiver station to the remote location (hereinafter "polling"). Polling is a costly approach because a receiver and transmitter combination is required at each location and must be receiving whenever a signal needs to be sent. Additionally, as transmitters are added, the polling time must be increased to accumulate all the transmitter time slots. The polling function looks for signals sent in a prescribed order, such that a given signal sent from a corresponding specific location takes a place in line other than the order in which it was sent or received.
It is further important to point out that all DA converter functions, including devices incorporating frequency modulation and pulsed width modulation, must operate within the limitations of the FCC regulations. The distinction between the two such devices is that pulsed width modulated devices place most of its power at the carrier frequency as compared to frequency modulated (i.e., shift keying) devices which use much of their power performing the polling function and signal verification and still be within FCC guidelines. The result is that the signals sent by pulsed width devices can be sent from a greater distance with greater degree of reliability as compared to frequency modulated devices. Devices incorporating frequency modulation uses a single frequency with two tones, e.g., 1200 and 1800 Hertz tones. The two different tones are frequency modulated on the carrier radio frequency signal and are used for positioning within the poll.
In addition, the "polling" or "time slotting" function of frequency modulated devices must include a time basis associated with various transmitter units (e.g., table units and the master units of the, for example, the Carlman invention). The time basis of the table and master units must be synchronized. This is required because the random transmission of signals from the table units initiates the coded start signal, which in turn synchronizes the table and master unit time bases so the polling function of the overall system allows the individual table signals to be received in a preselected order, an order other than the order in which the signals were sent, such that the physical identity of the location of the originating signal can be determined only through a comparison of the preselected order and the existence of a signal positioned within its one individual position.
In addition to the Carlman reference, the remote signalling devices comprising the art to which the invention relates further include:
U.S. Pat. No. 4,935,720 granted to Kalfoun, incorporated by reference as if fully set forth herein, is directed to an apparatus for the transmission of information in a restaurant.
U.S. Pat. No. 4,722,053 granted to Dubno et al. on Jan. 26, 1988, incorporated by reference as if fully set forth herein, is directed to a food service ordering terminal with video game capability.
U.S. Pat. No. 4,530,067 granted to Dorr on Jul. 16, 1985, incorporated by reference as if fully set forth herein, is directed to a restaurant management information control method and apparatus.
U.S. Pat. No. 4,222,111 granted to Sloan et al. on Sep. 9, 1980, incorporated by reference as if fully set forth herein, is directed to a method and apparatus for monitoring status of tables in a restaurant.
U.S. Pat. No. 3,962,689 granted to Brunson on Jun. 8, 1976, incorporated by reference as if fully set forth herein, is directed to a memory control circuitry.
U.S. Pat. No. 3,821,707 granted to Peters on Jun. 28, 1974, incorporated by reference as if fully set forth herein, is directed to a waitress call system for cocktail lounge, restaurant, or the like.
U.S. Pat. No. 3,665,313 granted to Trent on May 23, 1972, incorporated by reference as if fully set forth herein, is directed to a location identification system.
U.S. Pat. No. 3,439,320 granted to Ward on Apr. 15, 1969, incorporated by reference as if fully set forth herein, is directed to a personnel location system.
U.S. Pat. No. 3,310,797 granted to Auger on Mar. 21, 1967, incorporated by reference as if fully set forth herein, is directed to a method and apparatus for coordinating restaurant operation.
U.S. Pat. No. 1,796,668 granted to Sarfatty on Mar. 17, 1931, incorporated by reference as if fully set forth herein, is directed to a restaurant service system and apparatus.